Preliminary investigations have indicated that mosquito cells infected in Banzi virus (flavivirus) release a low molecular weight factor of viral origin which suppresses the replication of only Banzi virus in both mosquito and mammalian cells. We plan to purify this factor so that analysis of the factor by a variety of biochemical and immunological techniques can establish the relationship between this factor and Banzi viral proteins. Using preparations of purified factor, we will examine the effect of pH, salt concentrations and enzymatic treatment of its inhibitory action. In addition, we will attempt to determine whether this factor is responsible for homologous interference observed in persistently mosquito cells. The mechanism by which this factor regulates Banzi viral growth in mammalian cells and in mosquito cells by its effect on attachment of virus to cells, on viral protein and RNA synthesis and on assembly of virus will be examined. Finally, we will ascertain whether this factor is produced in persistently infected mammalian cells.